Lenovo ThinkPad 770 DVD Information Brief - Page 3

models. Great picture quality-720 horizontal pixels/line of resolution vs. 240 pixels for the VHS format- is enhanced by Dolby Digital sound (also known as AC-3™) delivering 5.1 audio, that is, 5 surround channels plus one sub-woofer channel. Other advantages allowed by DVD include: random access parental control of programs multiple aspect ratios (4:3, 16:9, pan-and-scan) 8 separate audio tracks for multiple language versions on the same disc 32 subtitle channels on the same disc In addition to alternate versions, such as the "director's cut," future viewers can enjoy alternate camera angles, and user-controlled branching for interactive story lines. As of this writing, more than 100 DVD movie titles are available, with about 600 expected by the end of 1997-everything from Ace Ventura: Pet Detective, to Doctor Zhivago. To whet your appetite, point your Web browser to www.dvdexpress.com for a complete listing. DVD-R (read/write-once) The next phase of the DVD technology rollout is expected to complement current CD-R technology. Write-once is currently used primarily by content providers and application developers and is considered to be a "special purpose" device. DVD-R will fill this niche and is expected to be introduced by late summer 1997. DVD-RAM (read/write many times) The third phase should be eventually priced as a consumer item and is intended to replace VCRs. DVD-RAM technology probably won't arrive until 1998, but has the potential to have a significant impact on the computer industry due to the high storage capacity of its discs, as well the ability to write to them many times. DVD-Audio As of this writing, standards have not been set for audio-only DVD. The disagreement centers mainly on sampling rates and the number of channels supported. Audiophiles want a higher sampling rate of 96KHz, compared to the current standard of 44.1KHz of audio CDs. Compressing Digital Video for DVD Even with the enormous storage capacity of DVD, digital video must be compressed to fit within the 4.7GB capacity of a single-side disc. Because DVD has standardized on MPEG compression of digital video, a summary of the technology follows. (For more details, see the Digital Video Information Brief.) The MPEG standards The MPEG standards are named after an International Standards Organization (ISO) subcommittee that developed them, the Moving Picture Experts Group. The standards provide a common world language for high-quality digital video. The MPEG compression process is asymmetrical (taking more time to compress than decompress), and requires serious computational power to reduce the file size. But the results are impressive. MPEG encoding is a lossy process, that is, some information is purposely sacrificed (lost) to reduce the file size. The discarded data is selected by a sophisticated algorithm based on human perception, eliminating only the visual information that our eyes usually ignore. The details of September 1997 3